Correlation between Raman spectroscopy and electron microscopy on individual carbon nanotubes and peapods

Spudat, Christian

Book	PreJuSER-136235

Correlation between Raman spectroscopy and electron microscopy on individual carbon nanotubes and peapods

Spudat, C. (Corresponding author)FZJ*

2010
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
ISBN: 978-3-89336-648-4

Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Information / information 11, XIV, 125 S. (2010) = Universität Duisburg, Diss., 2010

Please use a persistent id in citations: http://hdl.handle.net/2128/3815

Abstract: In this thesis, we investigate the possibility of filling carbon nanotubes (CNTs) grown by chemical vapor deposition (CVD) with guest molecules directly on substrates. This requires the characterization of CNTs after synthesis. It is shown by high-resolution TEM and Raman spectroscopy that the diameter distribution and number of layers of as-grown CNTs depends on the growth temperature T$_{CVD}$. HRTEM measurements are seen to induce defects, even when performed at electron energies as low as 80 keV. Raman spectroscopy, on the other hand, is non-destructive for individual CNTs at small laser intensities (P < 0.5mW). This fact motivated us to attempt a correlation of HRTEM and Raman spectroscopy, which allowed us to prove the radial phonon-coupling for an individual multi-walled CNT and a bundle of single-walled CNTs for the first time experimentally and to confirm our results by a simple numeric model. Furthermore, it could be shown that the width of the resonance profiles of radial Raman modes allows one to determine whether the investigated CNT is an individual single-walled CNT, located within a bundle or a layer of a multi-walled CNT. This makes a determination of the inter-molecular structure of CNTs possible without damaging the CNTs by TEM imaging. Moreover, resonant Raman spectroscopy provides important information about the electronic structure of the investigated CNTs, which is essential for interpreting future quantum transport measurements and permits the determination of the atomic structure of individual CNTs. A second part of this thesis deals with the synthesis of peapods, CNTs filled with fullerene molecules such as C60. We present a detailed characterization of individual CNTs after each step of the peapod synthesis, focusing especially on the opening of the as-grown CNTs. A UHV-chamber was built up to avoid reactions between the opened CNTs and the atmosphere, allowing for the in situ removal of excess fullerene molecules from the CNTs. Using this novel method, we obtain clean peapods in different yields and with different numbers of layers directly on the substrate, which opens the way for future quantum transport measurements of these systems.

Keyword(s): carbon ; nanotube ; transmission electron microscopy ; raman spectroscopy ; phonon ; electronic structure ; transport theory